Copper and nickel concentrates are usually processed in a smelter which melts the concentrate to form a metallic matte and a slag essentially composed of iron silicate containing small amounts of valuable metals such as copper, nickel and cobalt.
In Canada, smelters produce over 12 million tons of iron silicate slags often containing up to about 0.7% copper, 1% nickel and 0.25% cobalt. Since 1900, some uses for these slags have been found, such as for rail ballast, road base and backfill, but such known uses have not been sufficient to utilize the amount of slag produced.
Considerable research has been carried out to attempt to lessen the amount of metals lost in the slag and/or to recover these metals from the slag. So far as is known, no economically viable process has been found to recover these lost metals, and as a result large slag heaps have accumulated adjacent to the smelters.
As water pollution control standards have developed, it has been found that the large slag heaps are leaching unacceptably high amounts of heavy metals, and mining companies are seeking acceptable solutions to this growing problem. Also, environmental authorities are demanding that plans be filed with the appropriate government agencies to provide commitments for long term permanent solutions to this problem.
It is therefore an object of the invention to provide a method of treating base metal smelter slag to recover metals and produce a secondary slag.